1. Field of the Invention
This invention relates to an improvement in and relating to a tubular organic prosthesis composed of a porous tubing of polytetrafluoroethylene (to be abbreviated "PTFE"), and is directed to increasing the strength of the tubing and its ability to connect with the tissues of patients.
2. Description of the Prior Art
Many reports have been made heretofore to show that a porous tubing of PTFE produced by a stretching method can be clinically used as a tubular organic prosthesis, especially as a vascular prosthesis. Such a prosthesis is regarded as better than conventional prostheses made of knitted or woven fabrics. A PTFE tubing which has been subjected to a stretching treatment has a microstructure composed of very fine fibers and nodes connected to one another by the fibers. The diameters of the fibers vary depending on stretching conditions, and can be made much smaller than those of the fibers of the knitted or woven fabrics mentioned above. Moreover, since the pore diameter and porosity of the tubing can be varied freely, when it is used, for example, as an artificial vessel, it is pliable and scarcely permits formation of thrombus. The tubing also shows good formation of a pseudointima on the inner surface without any appreciable adverse effect on the surrounding tissues. Thus, the stretched PTFE tubing is regarded as one of the best tubular organic prostheses.
The stretched PTFE tubing, however, has the disadvantage that when it is used as a tubular organic prosthesis and joined with the living body the needle or suture tends to tear the tubing. This tearing frequently occurs in the axial direction of the porous PTFE tubing. Since this is due to the orientation of the fine PTFE fibers formed as a result of stretching, it can be reduced to some extent by biaxially stretching the tubing, namely stretching it in the axial direction and expanding its diameter, thereby to change the structure of the fine fibers to a radial orientation. A great improvement in strength, however, cannot be expected from this process alone. Furthermore, it is difficult for natural occlusion of suture holes to occur based on the elasticity of the porous PTFE tubing alone, and when used as an artificial vessel, bleeding from the suture holes is also a problem.
The present invention offers a solution to these problems in a junction operation.